1. Field of the Invention
The present invention relates to a magnetic detector for detecting a magnetic field that is generated from a multi-polarized rotor with the use of a magnetic resistance element (MR element) and, more particularly, to a structure of a magnetic detector in which a bias magnetic field is applied to the magnetic resistance element.
2. Description of the Related Art
FIGS. 10(a), (b) and (c) are drawings of a conventional magnetic detector shown, for example, in the Japanese Patent Publication (unexamined) No. 69546/2004. Specifically, FIG. 10(a) is a perspective view conceptually showing a constitution of the conventional magnetic detector. FIG. 10(b) is a diagram taken from a viewpoint P of FIG. 1(a). FIG. 10(c) is a characteristic chart showing a relation between a distance L from the centerline of a bias magnetic field applied to the magnetic resistance element and a bias magnetic field.
Further, FIGS. 11(a), (b), (c), (d) and (e) are timing charts showing operations of the conventional magnetic detector shown in FIG. 10.
In addition, as described later, FIG. 11 also show operations of a magnetic detector according to the invention.
With reference to FIG. 10(a), reference numeral 100 designates a rotor, being a detected body that is multi-polarized. For example, this rotor is a rotary disc provided with a plurality of polarized protrusions at a circumferential portion thereof.
Numerals 30a to 30d designate magnetic resistance elements (they are referred to as magnetic resistance segments as well). Numeral 31 designates a signal processing circuit section in which a circuit is printed on the surface of a board. Numeral 5 designates a magnet. Numeral 90 designates a rotary axis on which the rotor 100 rotates. Numeral 2 designates a magnetic guide.
The magnetic guide 2 functions to correct a direction of lines of magnetic force so that the lines of a magnetic force generated from the magnet 5 efficiently pass through the magnetic resistance elements 30a to 30d. 
Additionally, with reference to FIG. 10(a), although the magnetic resistance elements 30a, 30d and the magnetic resistance elements 30b, 30c are indicated by one black block, this is due to the fact that respective magnetic resistance elements densely massed, and each element cannot be illustrated apart from each other.
As shown in FIG. 10(b), the magnetic resistance elements 30a to 30d are disposed on the signal processing circuit section 31 on the side of the rotor 100 in such a manner as to be away from the centerline (in parallel to the rotary axis 90) in a polarization direction of the magnet 5 by a distance L.
In addition, the signal processing circuit section 31 outputs signals responsive to multi-polarization of the rotor 100 based on the change in resistance value of the magnetic resistance elements 30a to 30d due to change in magnetic field.
Further, with reference to FIG. 10(c), an axis of abscissas indicates a distance L from the centerline of a bias magnetic field provided by the magnet 5; and an axis of ordinates indicates a bias magnetic field (applied magnetic field) to be applied to the magnetic resistance elements.
As shown in FIG. 10(b) and FIG. 10(c), in the magnetic circuit of the conventional magnetic detector, it is possible to appropriately adjust a bias magnetic field with respect to the magnetic resistance elements based on the distance L from the centerline of the magnet 5.
FIG. 11 are timing charts for explaining operations of the magnetic detector shown in FIG. 10.
In the drawings, FIG. 11(a) indicates condition of change in magnetic poles coming close to the magnetic resistance element part (magnetic resistance elements 30a to 30d) due to the fact that the multi-polarized rotor 100 rotates.
Further, FIG. 11(b) shows condition of change in magnetic fields to be applied to the magnetic resistance elements 30a, 30d. FIG. 11(c) indicates condition of change in resistance values of the magnetic resistance elements 30b, 30c. FIG. 11(d) indicates condition of change in output from the later-described differential amplifier circuit of the signal processing circuit section 31. FIG. 11(e) indicates condition of change in final output from the signal processing circuit section 31.
Thus, according to the conventional magnetic detector shown in FIG. 10, output signals corresponding to multi-polarization of the rotor 100 can be obtained.
That is, rotational operation of the rotor 100 that is multi-polarized can be detected.
The above-described conventional magnetic detector includes the magnetic resistance elements 30a to 30d that detects a change in magnetic fields of the rotor 100 that is multi-polarized; the signal processing circuit section 31 that outputs signals corresponding to multi-polarization of the rotor 100 based on a resistance value of the magnetic resistance elements 30a to 30d due to the change in magnetic fields; the magnet 5 that applies a bias magnetic field to the magnetic resistance elements 30a to 30d; and the magnetic guide 2 that corrects a direction of the lines of magnetic force generated from the magnet 5.
In such a conventional magnetic detector, respective magnetic resistance elements, signal processing circuit section, magnet, and magnetic guide forming a magnetic circuit are components each separately independent of each other.
Accordingly, a problem exists in that number of parts is large, and many processes of assembling are required at the time of manufacturing, whereby any efficient production cannot be carried out.
Moreover, individual parts are manually assembled, so that relative positional accuracy in individual parts at the time of assembling is likely to be negatively affected.
Consequently, in completed product, the fluctuation in characteristics such as magnetic detection accuracy of the multi-polarized rotor cannot be diminished, going beyond a certain level.